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Optical coatings are well-known in the art. In this regard, optical coatings are frequently utilized to enhance performance of optical systems. Moreover, such coatings can be specially designed and fabricated to produce greater accuracy and reproducibility as may be needed for a given application. In this respect, such films can serve as mechanical and/or chemical protective barriers, as disclosed in U.S. Pat. No. 4,632,844 to Yanagihara, and may further have high transmissivity in the infrared spectral region, as disclosed in U.S. Pat. No. 5,830,873 to Benz et al.
Typically, optical coatings are formed by vacuum deposition upon the substrate sought to be coated. Advantageously, by depositing such materials under vacuum conditions, there thus may be controlled the purity, deposition rate and micro-structure of the resultant optical coating. In fact, such deposition processes have been so refined that precise control of coating thickness, as well as the refractive index possessed thereby, can be achieved and consistently reproduced. For example, it has long been known that glow discharge and organic vapor or gas can be used to produce thin, optically transparent films, as disclosed in U.S. Pat. No. 3,822,922 Smolinski et al. Along these lines, it is also well-known that changes and the parameters of such deposition processes can produce modest changes in infractive index, as disclosed in U.S. Pat. No. 5,217,749 to Denton et al.
Moreover, due to the control of thickness and index of refraction that may be attained via vacuum deposition, multi-layer optical coatings can be fabricated to optimize reflection, transmission and absorption of light. It is further known in the art to construct multi-spectral coatings, although it is recognized that as spectral requirements increase, coating complexity increases. Along these lines, infrared multi-spectral coatings with 50 to 100 layers totalling 10 to 20 microns thick are not uncommon.
Generally, materials utilized for optical coatings do not possess high flexibility and most prior art coating systems have been limited in applications involving hard, stable optical substrates. In this respect, traditional optical coating materials comprise metals, semi-conductors, oxides and fluorides. While some degree of flexibility is attainable when such materials are very thin, optically useful thicknesses are generally not sufficiently flexible. In the case of metallic reflectors, however, it is known that some metals can be deposited thin enough to provide flexibility and high reflectance, although such class of coating materials is considered the exception as opposed to the general rule.
Along these lines, it is known that the flexibility properties of optical coatings are compromised at the expense of the reflectivity of such coating materials. Although otherwise well-suited, metallic reflectors are negated in some applications by other requirements or considerations, such as spectral filtering and/or microwave remittance, for example, which, as a consequence, require multi-layer dielectric design. Unfortunately, such dielectric reflector and multi-spectral coatings require much thicker layers and are not considered flexible, as would otherwise be desired.
As such, there is a considerable need in the art for fabrication processes by which optical coatings can be formed having sufficient durability concerning a variety of aspects, and in particular, material friability, hardness, internal stress and adhesion. Such durability concerns are further affected by the properties of the coating substrate. With respect to the latter, it is known in the art that optical coating durability plays less of a consideration when hard, stable substrates are utilized. Flexible substrates, on the other hand, are not as forgiving and, as such, prevent traditional optical coatings from achieving sufficient durability when applied thereto.
There is additionally a substantial need in the art for a method of fabricating optical coatings that are highly durable and are capable of subsisting on flexible substrates as well as a need for a method of fabricating optical coatings that, in addition to possessing a high degree of durability, further possesses excellent adhesion properties and can be selectively modified to produce an optical coating having a desired index of refraction.
Still further, there is a need for processes for fabricating optical coatings that may be readily and easily practiced, are inexpensive to deploy, can be utilized to form multi-layer coatings and can be utilized for a broad range of applications involving light having a wave length falling within the spectral range of visible to long-wave infrared light.
The present invention specifically addresses and alleviates the above-identified deficiencies in the art. In this regard, the present invention is directed to optical coatings and methods of forming optical coatings that have superior durability than prior art coatings and, in particular, may be applied to and effectively utilized with highly flexible substrates. According to the preferred embodiment, the coatings of the present invention comprise thin polymeric films formed-by the disassociation of chemical subcomponents from gaseous hydrocarbons in plasma which possess a low index of refraction, as well as a sufficiently low extinction coefficient. The disassociation process is conducted under low pressure and without radio frequency substrate bias, similar to processes utilized in depositing diamond-like-carbon.
The resultant coatings may be utilized on a variety of substrates, including highly flexible substrates such as urethane. The coatings may further be utilized in applications involving light ranging from visible to long-wave infrared. Such optical coatings and methods of fabricating the same may further be utilized to form coatings having a specified thickness sufficient to realize multi-layer optical designs. To the extent it is desired to cause the coating formed to possess index contrasts, as may be required for multi-layer optical designs, the polymeric film formed from the disassociation of the gaseous hydrocarbon in plasma may be doped with a polar material, such as germanium or silicon, which consequently raises the index of refraction for the optical coating. According to the preferred embodiment, such polymer material is sputter deposited in the growing polymer as the same is deposited upon the optical substrate.
It is therefore an object of the present invention to provide optical coatings and methods of fabricating the same that are highly durable, stable and exceptionally flexible such that the same may be utilized on highly flexible substrates.
Another object of the present invention is to provide optical coatings and methods of fabricating the same that, in addition to having superior durability and flexibility, may be utilized for multi-layer optical designs, and may be further formed to have a desired index of refraction.
Still further objects of the present invention include providing optical coatings and methods of manufacturing the same that may be readily and easily formed by utilizing existing, commercially available materials, are efficient to fabricate, may be utilized on any of a variety of substrates, and may be utilized for any of a variety of applications utilizing light ranging from visible through long-wave infrared.